The present invention relates to a method for producing an electrode material for vacuum circuit breaker, an electrode material for vacuum circuit breaker, and an electrode for circuit breaker. The invention relates particularly to a method for producing an electrode material of an alloy of molybdenum (Mo)-chromium (Cr) for a vacuum circuit breaker of high-voltage with large capacity that has a good interruption performance.
A vacuum circuit breaker has a cylindrical insulative container of ceramic that is capable of maintaining its inside vacuum. The container arranges two electrodes facing each other in a coaxial arrangement. One electrode works as a fixed side electrode and the other works as a moving side electrode. The container and the electrodes so arranged compose the main body of a circuit breaking valve in the vacuum circuit breaker. The circuit breaking valve interrupts current by movement of the electrodes, wherein the electrode on the moving side is moved toward circuit-opening direction by an operating mechanism installed in the vicinity of the main body of the valve.
As Japanese Laid-open Patent Application No. 2003-92050 (Patent literature 1) and Japanese Laid-open Patent Application No. 2010-113821 (Patent literature 2) for example describe, electrodes in vacuum circuit breakers of recent days have such structure that each of those electrodes, on the fixed side and the moving side, generates an axial magnetic field when arcing occurs. When such electrode of the moving side moves to open the circuit, the electrodes, i.e., the fixed side electrode and the moving side electrode, separate and stay at the redetermined separation position to disperse the arc appeared across the electrodes in the circuit-open position by the axial magnetic field making it possible to interrupt high currents.
Each electrode of axial magnetic field type is comprised of a cup-shaped contact member fixed on the end face of a conductive rod and a contact plate as an arcing portion, is firmly fixed on the end face of the conductive rod. The outer periphery of the cup-shaped contact member, which outer peripheral part is on the opposite side of the conductive rod, has a plurality of slits that are slant with respect to the axis. These slits in such configuration form a plurality of current paths namely what is called a coil portion. When the electrode of axial magnetic field type on the moving side is moved toward circuit-opening direction, use of such cup-shaped contact member causes the current flowing through the coil portion to generate the axial magnetic field; thereby arc ignited on the contact plate is dispersed and the current is interrupted.
In a vacuum circuit breaker of high-voltage with large capacity, each electrode of axial magnetic field type thereof, which repeats movements for contacting and separating, uses material with a good electrical performance in such as the current interruption performance and the withstand voltage performance as the electrode material for the contact plate that works as the contact face. In general, electrode materials for vacuum circuit breakers are sintered compacts manufactured by a method comprising: mixing copper (Cu), as a material having good conductivity, and such as Cr or Mo, as an arc-resistant component, at a predetermined ratio to obtain a mixture; pressing and molding the mixture; and sintering the press-molded mixture in a non-oxygen atmosphere such as vacuum.
For example, Japanese Patent Gazette No. 3926994 (Patent literature 3) has proposed an electrode material of sintered compact, wherein, in manufacturing a Cu—Cr based material as an electrode material with good electrical performance in such as the current interruption and the withstand voltage performance, the sintered compact is obtained by processing a mixture of Cu, as the base material, and Cr, as the electrical performance improving constituent, and heat resisting elements that makes Cr particles fine.
The specified range of composition of the proposed electrode material is, in terms of weight ratio, Cu 20 to 80%, Cr 10 to 80%, Mo 0.001 to 80%, tungsten (W) 0.01 to 80%, tantalum (Ta) 0.001 to 80%, niobium (Nb) 0.001 to 80%, and vanadium (V) 0.001 to 80%.
Japanese Laid-open Patent Application No. 2002-15644 (Patent literature 4) proposes a highly reliable contact material for a vacuum circuit breaker in which welding and wear of the contact material is little and arcing resistance performance is improved and contact resistance is low. The proposed contact material contains a highly electro-conductive component composed of at least one kind of Cu, silver (Ag), and gold (Au) whose content is from 20 to 45 wt %, and an arc-resistant component composed of at least one kind of W, Mo whose content is from 55 to 80 wt %. The literature further describes such a feature that metal texture of this contact material has a scatter of the highly electro-conductive phase having a maximum cross-sectional area sized from 0.001 to 0.005 mm2. The literature also proposes a processing in which the highly electro-conductive component is infiltrated into holes in a sintered compact at the final stage of the manufacturing.
As Patent literature 3 mentioned above describes, to improve electrical performance of an electrode material for vacuum circuit breaker in such as the current interruption performance against fault currents (hereinafter referred to as “high current interruption performance”) and withstand voltage performance, it is effective to increase content amount of high melting point materials such as Cr and Mo in the Cu substrate of Cu-based electrode material, and to use Cr, etc. having fine grain size, and to disperse them homogeneously. However, excessive increase in content amount of high melting point materials such as Cr and Mo decreases the content amount of Cu in the electrode material for vacuum circuit breaker. This causes the conductivity of the material to be lowered and consequently the contact resistance increases with the high current interruption performance lowered. Further, such excessive increase invites a disadvantage in that the interruption performance in the cutting-off of capacitive loads (hereinafter referred to as “capacitor switching performance”) will be not satisfied. Moreover, as Patent literature 4 describes, the high current interruption performance or the capacitor switching performance is lowered in particular for the electrode material of Cu—W system that is manufactured by mixing Cu powder and W powder; this prevents the material from being applied to vacuum circuit breakers.
It is well known that the content of high melting point material such as Cr in an electrode material for a vacuum circuit breaker for high-voltage with large capacity needs to be increased. However on the other hand, there has been a problem with such electrode material in that the increased amount lowers the high current interruption performance and increases the contact resistance.
Moreover, when the impulse voltage (hereinafter abbreviated as “IMP” for short) property of the contact plate of the electrode at the time of the current interruption of a vacuum circuit breaker is examined, it is revealed that electric field intensity around the periphery of the contact plate at the time of arcing is high causing concentration of electric field, which will easily develop to an IMP withstand voltage breakdown. For this reason, in the vacuum circuit breaker that uses an electrode of axial magnetic field type, improvement in IMP withstand voltage of the contact plate and more improvement in the high current interruption performance and the capacitor switching performance are desired.
In addition, when the contact plate is formed using a material such that Cu is infiltrated into Mo—Cr alloy with content amount of Mo increased, the electron emission due to the electric field will increase and discharge due to IMP will occur in the intense electric field area, incurring a disadvantage of the withstand voltage against IMP being lowered. Moreover, when the contact plate of the electrode of axial magnetic field type is formed using only Cu—Cr alloy of a good IMP performance having increased content amount of high melting point material such as Cr, the high current interception performance and the capacitor switching performance will be lowered.
An object of the present invention is to provide a method for producing an electrode material for vacuum circuit breaker and an electrode material for vacuum circuit breaker, wherein the electrode material is capable of improving the withstand voltage, the high current interruption performance, and the capacitor switching performance even if the content amount of the arc-resistant component in the electrode material is increased.
Another object of the present invention is to provide an electrode for vacuum circuit breaker that is capable of improving IMP withstand voltage together with improving the high current interruption performance and the capacitor switching performance.